Engineering plastics are superior in strength, elasticity, and thermal stability as well as chemical resistance and electrical insulation, as compared to general-purpose plastics. Accordingly, the engineering plastics have recently been applied to various industrial fields such as household goods, electrical and electronic products, and aircraft structural materials and various studies are being actively conducted on the engineering plastics as candidate materials that can replace metals.
Engineering plastics may be classified into general engineering plastics including five general-purpose engineering plastics with high usage and high-performance engineering plastics with excellent heat resistance. However, these high-performance engineering plastic materials have a higher production cost than other plastics in spite of their excellent performance. Thus, unlike general-purpose plastics which are easy in mass produce, the high-performance plastic materials are mainly focused on customized development and production required for end use.
As a result, actual applications of high-performance plastic materials have been quite limited up to now due to their relatively lower high-temperature mechanical properties than metal materials in automobile parts and turbine materials for metal replacement which may be most demanding.
Carbon fibers are low-cost reinforced materials which are light and strong, have a high modulus of elasticity, and are also widely used in general-purpose plastics including engineering plastics.
In general, commercially available plastics including engineering plastics are provided as carbon fiber/plastic composites with carbon fiber added. Strength improvement of several times to several tens of times may be achieved depending on the amount of the carbon fiber added. Carbon fibers may be used by mixing various types of carbon fibers such as PAN-based carbon fibers, Pitch-based carbon fibers, and Rayon-based carbon fibers according to the types of plastic such as thermosetting and thermoplastic.
Each carbon fiber is subjected to a sizing treatment to coat the carbon fiber with an interfacial binder to achieve a stable physical interface between plastic resins. When a composite material is prepared by mixing the sizing-treated carbon fiber with a plastic, the composite material exhibits very excellent reinforcing effect at room temperature but exhibits very low interfacial stability between a plastic base material and a surface of the carbon fiber at high temperature. For this reason, high-temperature reinforcing effect is negligible, which is not suitable as a reinforcing method for high heat-resistance engineering plastics.
To overcome these disadvantages, applying a solvent solution of a sizing agent containing a polyglycidyl ether to a carbon fiber as a method for modifying a carbon fiber surface is disclosed (Patent Document 1). However, the method is not preferable due to probability of environmental contamination caused by addition of acid or chemical.
In addition, a method for modifying a surface of a carbon fiber using atmospheric pressure plasma during the production of the carbon fiber is disclosed (Patent Document 2). However, the method is limited in using excellent characteristics of a pure carbon fiber because a nano-thin film is formed on a surface of the carbon fiber.
A technology proposed in the present disclosure to overcome the above-described disadvantages reduces the manufacturing cost through an environment-friendly and simple process by plasma-treating a commercially available carbon fiber and induces mechanical and chemical bonding between a plastic and a carbon fiber by modifying a surface of the carbon fiber and providing a functional group to improve mechanical characteristics. Accordingly, the technology is aimed at securing stable mechanical properties even at high temperature to widen its use range.
Patent Document 1: Japanese Patent Publication No. 50-59589
Patent Document 2: Korean Patent Publication No. 10-2012-0055042